Radio wave reflecting device

Abstract

This radio wave reflecting device includes a plurality of radio wave reflecting elements arranged in a matrix having a plurality of rows and a plurality of columns. Each of the plurality of radio wave reflecting elements has a patch electrode, a first alignment film on the patch electrode, a liquid crystal layer on the first alignment film, a second alignment film on the liquid crystal layer, and a common electrode positioned on the second alignment film. The patch electrode has a plurality of first slits, and the plurality of first slits are parallel to each other, have the same width, and extend in one of the row direction and the column direction. The common electrode has a plurality of second slits, and the plurality of second slits are parallel to the plurality of first slits and have the same width. In each of the plurality of radio wave reflecting elements, the distance between the adjacent first slits is constant, and is the same as the distance between the adjacent second slits.

Description

radio wave reflector

[0001] One embodiment of the present invention relates to a radio wave reflecting device.

[0002] Because liquid crystal molecules have a dielectric anisotropy, the dielectric constant of the liquid crystal layer can be controlled by adjusting the electric field applied to the liquid crystal layer, thereby controlling the orientation of the liquid crystal molecules. Taking advantage of this property, metasurfaces that can control the reflection characteristics of the liquid crystal layer with respect to radio waves are known (see, for example, Patent Documents 1 and 2).

[0003] JP 11-103201 A JP 2019-530387 A

[0004] An object of one embodiment of the present invention is to provide a radio wave reflecting device having a new structure, or to provide a radio wave reflecting device that is both transparent to visible light and has excellent radio wave reflecting characteristics.

[0005] One embodiment of the present invention is a radio wave reflecting device. The radio wave reflecting device includes a plurality of radio wave reflecting elements arranged in a matrix having a plurality of rows and a plurality of columns. Each of the plurality of radio wave reflecting elements includes a patch electrode, a first alignment film on the patch electrode, a liquid crystal layer on the first alignment film, a second alignment film on the liquid crystal layer, and a common electrode on the second alignment film. The patch electrode has a plurality of first slits, which are parallel to each other, have the same width, and extend in one of the row direction and the column direction. The common electrode has a plurality of second slits, which are parallel to the plurality of first slits and have the same width as the plurality of first slits. In each of the plurality of radio wave reflecting elements, the distance between adjacent first slits is constant and is the same as the distance between adjacent second slits.

[0006] 1 is a schematic exploded perspective view of a radio wave reflecting device according to an embodiment of the present invention; FIG. 2 is a schematic top view of a radio wave reflecting device according to an embodiment of the present invention; FIG. 3 is a schematic plan view of an opposing substrate of a radio wave reflecting device according to an embodiment of the present invention; FIG. 4 is a schematic plan view of an opposing substrate of a radio wave reflecting device according to an embodiment of the present invention; FIG. 5 is a schematic top view of a patch electrode of a radio wave reflecting element according to an embodiment of the present invention; FIG. 6 is a schematic top view of a common electrode of a radio wave reflecting element according to an embodiment of the present invention; FIG. 7 is a schematic end view of a radio wave reflecting element of a radio wave reflecting device according to an embodiment of the present invention; FIG. 8 is a schematic end view showing the arrangement of the patch electrode and the common electrode of a radio wave reflecting device according to an embodiment of the present invention; FIG. 9 is a schematic end view showing the arrangement of the patch electrode and the common electrode of a radio wave reflecting device according to an embodiment of the present invention; FIG. 10 is a schematic end view showing the arrangement of the patch electrode and the common electrode of a radio wave reflecting device according to an embodiment of the present invention; 1A and 1B are schematic top and end views of a model element 1 evaluated in the examples; 1C are schematic top and end views of model elements 2 to 4 evaluated in the examples; 1D are simulation results in the examples;

[0007] Hereinafter, various embodiments of the present invention will be described with reference to the drawings, etc. However, the present invention can be embodied in various forms without departing from the spirit of the present invention, and should not be construed as being limited to the description of the embodiments exemplified below.

[0008] In order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention. In this specification and each drawing, elements having the same functions as those explained in the previous drawings may be assigned the same reference numerals, and duplicate explanations may be omitted.

[0009] In this specification and claims, when expressing an aspect of placing another structure on top of a certain structure, the term "on top" is used, unless otherwise specified, to include both a case where another structure is placed directly on top of a certain structure so as to be in contact with the certain structure, and a case where another structure is placed above a certain structure via yet another structure.

[0010] In this specification and claims, the expression that two structures are "parallel" includes an embodiment in which the extension directions of the two structures are at an angle of 0° to each other and do not intersect, as well as an embodiment in which these extension directions are at an angle of within ±10°.

[0011] 1. Configuration of the Radio Wave Reflector The configuration of a radio wave reflector, one embodiment of the present invention, is described below. This radio wave reflector is a so-called liquid crystal metasurface reflector, a device that utilizes the change in dielectric constant caused by the orientation change of a liquid crystal layer due to an electric field to reflect irradiated radio waves in any direction. There are no restrictions on the wavelength frequency that can be reflected, for example, in the range of 400 MHz to 50 GHz. Typically, this radio wave reflector can be used to reflect radio waves in the 400 MHz to 6.0 GHz band, the 2.5 GHz to 4.7 GHz band, and the 24 GHz to 50 GHz band.

[0012] (1) Overall Structure: FIG. 1 shows a schematic exploded perspective view of a radio wave reflecting device 100. The radio wave reflecting device 100 has a substrate 102 and an opposing substrate 104, with various patterned insulating films, semiconductor films, and conductive films formed between them. By appropriately stacking these films, various wirings and multiple radio wave reflecting elements arranged in a matrix shape with multiple rows and columns are formed. As will be described in detail later, each radio wave reflecting element basically comprises a patch electrode 122, a common electrode 130, and a liquid crystal layer disposed between them. Wiring (not shown) extends from the radio wave reflecting element on the substrate 102 and is exposed at the edge of the substrate 102 to form a terminal 110. Power and various signals are supplied from an external circuit (not shown) via the terminal 110, and the radio wave reflecting element is controlled based on these signals. Radio waves enter from the substrate 102, are reflected by the radio wave reflecting element, and are emitted toward the substrate 102.

[0013] 2 to 3B show schematic top and plan views of the radio wave reflecting device 100. FIG. 2 is a schematic top view of the radio wave reflecting device 100 with the opposing substrate 104 removed, and FIGS. 3A and 3B are schematic plan views including the opposing substrate 104 as viewed from the substrate 102 side. As shown in FIG. 2, a plurality of patch electrodes 122 are formed on the substrate 102 in a matrix configuration with multiple rows and columns. To efficiently reflect both vertically and horizontally polarized radio waves, each patch electrode 122 preferably has two axes of symmetry parallel to the row and column directions. For this reason, the shape of each patch electrode 122 is preferably a regular n-gon such as a square (n is an integer or even number greater than 4), a circle, or a square, in particular. Multiple patch electrodes 122 located in the same column or row are electrically connected to each other via connecting portions 122a, resulting in equipotential configuration. In the example shown in FIG. 1, the multiple patch electrodes 122 located in each column are electrically connected to each other via connecting portions 122a. The potentials of the multiple patch electrodes 122 are controlled by signals supplied via the terminals 110. The signals supplied to the patch electrodes 122 are DC voltage signals or polarity-inverting signals in which DC voltages of different polarities are alternately inverted.

[0014] On the other hand, the common electrode 130 may be configured as a single electrode overlapping all patch electrodes 122 and shared by all radio wave reflecting elements 120, as shown in FIG. 3A , or as a plurality of electrodes arranged in a matrix shape having multiple rows and multiple columns so as to overlap each patch electrode 122, as shown in FIG. 3B . In the latter case, similar to the patch electrodes 122, the common electrodes 130 located in the same column may be electrically connected to each other, as shown in FIG. 3B . Alternatively, the common electrodes 130 located in the same row may be electrically connected to each other, as not shown. Alternatively, all the common electrodes 130 may be electrically connected to each other. In either case, unlike the patch electrodes 122, the same constant potential is applied to all the common electrodes 130 via the terminal 110. This potential is the ground potential or a potential corresponding to the intermediate level of the polarity inversion signal. When multiple common electrodes 130 are provided opposite each patch electrode 122 (Figure 3B), the shape of the common electrodes 130 is preferably a regular n-gon such as a square or a circle, similar to the patch electrodes 122, and more preferably has the same shape as the patch electrodes 122.

[0015] The substrate 102 and the counter substrate 104 are fixed to each other by a sealant 106, and a liquid crystal layer (described later) sandwiched between a pair of alignment films is provided in a space formed by the substrate 102, the counter substrate 104, and the sealant 106. The pair of patch electrodes 122, the counter substrate, the pair of alignment films, and the liquid crystal layer between the pair of alignment films form one radio wave reflecting element 120. Each component of the radio wave reflecting element 120 will be described in detail below.

[0016] (2) Substrate The substrate 102 and the counter substrate 104 are provided to impart physical strength to the radio wave reflecting device 100 and to provide a surface for arranging the radio wave reflecting element 120. The substrate 102 and / or the counter substrate 104 may be flexible. The substrate 102 and the counter substrate 104 include an inorganic insulator such as glass or quartz, or a polymer such as polyimide, polycarbonate, or polyester, and are configured to transmit visible light.

[0017] (3) Patch Electrodes The detailed structure of each patch electrode 122 will be described using the schematic top view of FIG. 4 . FIG. 4 shows one patch electrode 122 and portions of two patch electrodes 122 connected to this patch electrode 122 via connecting portions 122 a. As shown in FIG. 4 , each patch electrode 122 has multiple slits 122 b arranged parallel to each other. Here, a slit is an opening with a large aspect ratio provided in a film, and its outline has a closed shape formed by the film. The direction in which the slits 122 b extend may be the row direction or the column direction, or may be inclined from the row direction or the column direction. For example, as shown in FIG. 4 , the direction in which the slits 122 b extend may be parallel to the direction in which the multiple patch electrodes 122 electrically connected to it extend, or, although not shown, may be perpendicular. However, the direction in which the slits 122 b extend is the same between the patch electrodes 122.

[0018] The aspect ratio of each slit 122b, i.e., the length (longitudinal length) relative to the width (length perpendicular to the longitudinal direction), can be determined arbitrarily, for example, between 3 and 500, or between 10 and 200. The width of the slits 122b is set to between 0.1 μm and 100 μm. Furthermore, in each patch electrode 122, the widths of the multiple slits 122b are the same, and the multiple slits 122b are arranged at regular intervals. Therefore, if the width of the slits 122b in each patch electrode 122 is the space width S1 and the distance between adjacent slits 122b is the line width L1 (see FIG. 4), the line-space ratio (L1 / S1), i.e., the ratio of the distance to the width of the slits 122b, is constant within each patch electrode 122. Furthermore, L1 / S1 is the same across all patch electrodes 122. Furthermore, L1 / S1 is set to a relatively low value. Specifically, L1 / S1 is set to 0.05 or more and 4.0 or less, or 0.05 or more and 1.0 or less. Therefore, the space width S1 may be equal to or greater than the line width L1. By setting L1 / S1 within the above range, the aperture ratio of each patch electrode 122 can be set over a wide range of 20% or more and 80% or less. In other words, it is possible to obtain a high aperture ratio of up to 80%. The number of slits 122b provided in each patch electrode 122 can be set appropriately depending on the size of the patch electrode 122 and the width of the slits 122b, and is at least 3 or more, preferably 5 or more and 200 or less.

[0019] The patch electrode 122 may be formed of a conductive oxide such as indium-tin oxide (ITO) or indium-zinc oxide (IZO), or may contain a metal (zero-valent metal) such as gold, silver, copper, aluminum, molybdenum, tungsten, titanium, or chromium, or an alloy containing one or more of these metals. The patch electrode 122 can be fabricated by forming a conductive oxide or metal film using a sputtering method or a chemical vapor deposition (CVD) method, and then shaping this film by photolithography. When the patch electrode 122 contains a metal, the metal film may be shaped so that the portions between adjacent slits 122b have a mesh shape. Alternatively, the patch electrode 122 may be formed using metal nanowires containing silver or gold. Configuring the patch electrode 122 to contain a zero-valent metal not only prevents voltage drops that occur when the radio wave reflecting device 100 is enlarged, but also allows for wider control of the reflection angle of incident radio waves.

[0020] (4) Common Electrode The structure of the common electrode 130 is similar to that of the patch electrode 122. FIG. 5 is a schematic top view of a portion of the common electrode 130, which is shared by all of the radio wave reflecting elements 120 and formed as a single electrode overlapping all of the patch electrodes 122, with the patch electrodes 122 indicated by dotted lines. As can be seen from FIG. 5, the common electrode 130 facing the multiple patch electrodes 122 has multiple slits 130a arranged parallel to each other. The extension direction of the slits 130a is parallel to the extension direction of the slits 122b. In other words, the common electrode 130 is composed of multiple electrodes arranged in a stripe pattern and electrically connected to each other.

[0021] The aspect ratio and width of the slits 130a may be the same as those of the corresponding slits 122b in the patch electrode 122, and may be the same among the radio wave reflecting elements 120. Furthermore, the multiple slits 130a are arranged at regular intervals in the common electrode 130. Therefore, if the width of the slits 130a in the common electrode 130 is the space width S2 and the distance between adjacent slits 130a is the line width L2 (see FIG. 5), the line-space ratio (L2 / S2), i.e., the ratio of the distance to the width of the slits 130a, is constant within the common electrode 130. Furthermore, the line-space ratio (L2 / S2) is set relatively low, between 0.05 and 4.0, or between 0.05 and 1.0. Therefore, the space width S2 may be equal to or greater than the line width L2. By setting L2 / S2 within the above range, the aperture ratio of the common electrode 130 can be set in a wide range of 20% to 80%, and depending on the setting value, it is possible to obtain a high aperture ratio of up to 80%. The number of slits 130a provided in the common electrode 130 can also be set appropriately depending on the size of the common electrode 130 and the width of the slits 130a, and is at least 3 or more, and preferably 5 to 30, in each radio wave reflecting element 120. The difference in number between the slits 130a and the slits 122b is 0 or 1.

[0022] Like the patch electrode 122, the common electrode 130 may be formed of a conductive oxide such as ITO or IZO, or may contain a metal or alloy that can be used for the patch electrode 122. The common electrode 130 can also be fabricated by forming a conductive oxide or metal film using a sputtering method or CVD method, and then shaping this film by photolithography. When the common electrode 130 contains a metal, the metal film may be shaped so that the portions between adjacent slits 130a have a mesh shape. Alternatively, the common electrode 130 may be formed using metal nanowires containing silver or gold. Configuring the common electrode 130 to contain a zero-valent metal not only prevents voltage drops that occur when the radio wave reflecting device 100 is enlarged, but also allows for wider control of the reflection angle of the incident radio wave.

[0023] (5) Alignment Film and Liquid Crystal Layer FIG. 6 shows a schematic diagram of the end face of the radio wave reflecting element 120 taken along the dashed line A-A' in FIG. 4. As shown in FIG. 6, a patch electrode 122 is provided on the substrate 102 directly or via an undercoat 116 of any desired configuration. The undercoat 116 is composed of one or more films containing a silicon-containing inorganic compound, such as silicon oxide or silicon nitride, and is provided to prevent impurities contained in the substrate 102 from penetrating into the liquid crystal layer 126. One of a pair of alignment films (hereinafter referred to as the first alignment film) 124 is provided on the patch electrode 122 so as to cover the patch electrode 122. Therefore, the first alignment film 124 may be in contact with the substrate 102 or the undercoat 116. The first alignment film 124 is provided to control the alignment of liquid crystal molecules constituting the liquid crystal layer 126 provided thereon. The first alignment film 124 can be provided continuously across multiple radio wave reflecting elements 120. In other words, the radio wave reflecting elements 120 can be provided so as to be shared by all the radio wave reflecting elements 120 without being separated between adjacent radio wave reflecting elements 120 .

[0024] The first alignment film 124 includes a polymer such as polyimide or polyester. The first alignment film 124 is formed by using a wet film formation method such as an inkjet method, a spin coating method, a printing method, or a dip coating method, and the surface thereof is subjected to a rubbing treatment. Alternatively, the first alignment film 124 may be formed by a photo-alignment treatment.

[0025] The liquid crystal layer 126 contains liquid crystal molecules. The structure of the liquid crystal molecules is not limited. Therefore, the liquid crystal molecules may be nematic liquid crystal, smectic liquid crystal, cholesteric liquid crystal, or chiral smectic liquid crystal. The thickness T of the liquid crystal layer 126 is, for example, 20 μm to 100 μm, or 30 μm to 75 μm. Although not shown, spacers may be provided within the liquid crystal layer 126 to maintain this thickness throughout the radio wave reflecting device 100. Note that if the above-described thickness of the liquid crystal layer 126 is adopted in a liquid crystal display device, the high responsiveness required for displaying moving images cannot be obtained, and it becomes extremely difficult to demonstrate the functions of the liquid crystal display device.

[0026] The common electrode 130 is provided on the opposing substrate 104 directly or via an optional overcoat 118. Like the undercoat 116, the overcoat 118 can be composed of one or more films containing a silicon-containing inorganic compound such as silicon oxide or silicon nitride, and is provided to prevent impurities contained in the opposing substrate 104 from penetrating into the liquid crystal layer 126. Like the first alignment film 124, the other of the pair of alignment films (hereinafter referred to as the second alignment film) 128 is also provided to control the alignment of liquid crystal molecules and covers the common electrode 130. The second alignment film 128 can also be formed to be continuous across adjacent radio wave reflecting elements 120 and shared by multiple radio wave reflecting elements 120. The first alignment film 124 and the second alignment film 128 are arranged so that the direction in which the first alignment film 124 aligns the liquid crystal molecules is parallel to that of the second alignment film 128. The first alignment film 124 and the second alignment film 128 align the liquid crystal molecules in a specific direction.

[0027] (6) Arrangement of Patch Electrode and Common Electrode As described above, the patch electrode 122 and the common electrode 130 have slits 122b and slits 130a of the same width, respectively, arranged at regular intervals, and the widths and intervals of the slits 122b and slits 130a are the same in the patch electrode 122 and the common electrode 130. Therefore, as shown in the schematic end view of Fig. 7A, the patch electrode 122 and the common electrode 130 can be arranged so that all of the slits 122b and slits 130a overlap each other in the vertical direction (the normal direction of the substrate 102 or the counter substrate 104). However, the arrangement of the patch electrode 122 and the common electrode 130 is not limited to this. 7B , the patch electrode 122 and the common electrode 130 may be arranged so that at least one slit 122 b of the patch electrode 122 overlaps in the vertical direction with a region between adjacent slits 130 a of the common electrode 130, and similarly, at least one slit 130 a of the common electrode 130 overlaps in the vertical direction with a region between adjacent slits 122 b of the patch electrode 122. Alternatively, as shown in FIG. 7C , the patch electrode 122 and the common electrode 130 may be arranged so that at least one slit 122 b of the patch electrode 122 overlaps in the vertical direction with a slit 130 a of the common electrode 130 and a region between adjacent slits 130 a, and similarly, at least one slit 130 a of the common electrode 130 overlaps in the vertical direction with a slit 122 b of the patch electrode 122 and a region between adjacent slits 122 b. Regardless of the arrangement, light with a certain range of incident angles can pass through the radio wave reflecting element 120, ensuring the light transmittance of the radio wave reflecting device 100.

[0028] 2. Operation of the Radio Wave Reflecting Device The operation of the radio wave reflecting device will be described using the schematic diagrams ( FIGS. 8A and 8B ) of the end faces along the dashed line B-B' in FIG. 2 . In the radio wave reflecting device 100 having the above-described configuration, the first alignment film 124 and the second alignment film 128 align the liquid crystal molecules in the same direction. Therefore, when no potential difference is applied between the patch electrode 122 and the common electrode 130, no vertical electric field is generated in the liquid crystal layer 126, and the liquid crystal molecules are splay-aligned. The alignment of the liquid crystal layer 126 is the same between the radio wave reflecting elements 120, and therefore the dielectric constant is also constant within the liquid crystal layer 126. Therefore, as represented by the dotted arc in FIG. 8A , the spread (phase) of the reflected wave generated by the reflection of radio waves incident from the patch electrode 122 side (solid white arrow in FIG. 8A ) on the surface of the patch electrode 122 is the same between the radio wave reflecting elements 120. As a result, the incident radio wave is specularly reflected by the radio wave reflecting device 100, giving a reflected wave (shown by the dotted white arrow in FIG. 8A) having the same angle of emergence as the angle of incidence.

[0029] In contrast, when a potential difference is applied between the patch electrode 122 and the common electrode 130, the generated vertical electric field causes the liquid crystal molecules to stand up and bend. At this time, if vertical electric fields of different strengths are generated between the radio wave reflecting elements 120, more specifically, between the rows or columns to which the patch electrodes 122 are electrically connected, the dielectric constant of the liquid crystal layer 126 changes for each row or column depending on the strength of the vertical electric field. As a result, as shown by the dotted arcs in Figure 8B, the phase of the reflected wave also changes for each row or column, and accordingly, the reflection direction of the incident radio wave (solid white arrow in Figure 8B) can be changed (see the dotted white arrow in Figure 8B). The reflection angle can be controlled by changing the strength of the vertical electric field formed in the radio wave reflecting element 120.

[0030] As described above, in the radio wave reflecting device 100, both the substrate 102 and the opposing substrate 104 are configured to transmit visible light. Furthermore, the patch electrode 122 and the common electrode 130 are formed with slits 122b and 130a, respectively, each having a width that allows visible light to pass through. Therefore, regardless of which of the arrangements shown in Figures 7A to 7C is adopted, the radio wave reflecting device 100 is transmissive to visible light. Furthermore, as shown in the examples, by appropriately adjusting the line-to-space ratios (L1 / S1, L2 / S2) of the slits 122b and 130a within the above-mentioned ranges, it is possible to achieve both a high aperture ratio and excellent radio wave reflection characteristics, even when the metal-containing patch electrode 122 and the common electrode 130 are formed with a thickness large enough to block visible light. This makes it possible to provide a radio wave reflecting device with high visible light transmittance and excellent radio wave reflection characteristics. Therefore, by applying the embodiments of the present invention, it is possible to provide a radio wave reflecting device that does not impair or significantly impair the scenery.

[0031] 3. Modifications In the radio wave reflecting device 100 described above, multiple patch electrodes 122 in the same row or column are electrically connected, so that the change in the dielectric constant of the liquid crystal layer 126 is controlled for each row or column. Therefore, although the reflection direction of radio waves can be changed, the change in the reflection direction is one-dimensional. That is, the incident radio waves are reflected at an angle rotated around an axis extending in the column or row direction of the multiple radio wave reflecting elements 120. However, the configuration of the radio wave reflecting device 100 is not limited to the above configuration, and the potential of the patch electrode 122 of each radio wave reflecting element 120 may be individually controlled. This allows the reflection direction to be changed two-dimensionally.

[0032] For example, as shown in the schematic top view of FIG. 9 , a plurality of patch electrodes 122 are arranged in a matrix so as to be electrically and physically independent from one another, and an element circuit for controlling the patch electrodes 122 is formed on each radio wave reflecting element 120, as described below. A gate line driving circuit 112 and a signal line driving circuit 114 for supplying various signals to the radio wave reflecting elements 120 are provided on the substrate 102. The gate line driving circuit 112 and the signal line driving circuit 114 may be formed of an insulating film, a semiconductor film, or a conductive film formed on the substrate 102, or may be formed by mounting an integrated circuit formed on a semiconductor substrate on the substrate 102. The number of gate line driving circuits 112 may be one or more. In the latter case, as shown in FIG. 9 , two gate line driving circuits 112 may be arranged on the substrate 102 so as to sandwich a plurality of radio wave reflecting elements 120 therebetween. The signal line driving circuit 114 may be arranged on one side of the substrate 102 on which the terminals 110 are provided.

[0033] A plurality of gate lines and a plurality of signal lines (not shown) extend from the gate line driving circuit 112 and the signal line driving circuit 114, respectively, and are electrically connected to the radio wave reflecting elements 120. Various signals for driving the radio wave reflecting elements 120 are supplied to the gate line driving circuit 112 and the signal line driving circuit 114 from an external circuit (not shown) via a plurality of terminals 110. The gate line driving circuit 112 and the signal line driving circuit 114 generate gate signals and control potentials based on the supplied signals and supply them to the radio wave reflecting elements 120. In this way, the plurality of radio wave reflecting elements 120 are independently controlled.

[0034] Fig. 10 shows a schematic end view of one radio wave reflecting element 120. An element circuit for controlling each radio wave reflecting element 120 is provided on the substrate 102. The configuration of the element circuit can be determined arbitrarily, and the element circuit may be formed by appropriately combining one or more transistors, one or more capacitive elements, etc. In the example shown in Fig. 10, one transistor 140 electrically connected to the patch electrode 122 of the radio wave reflecting element 120 is shown as one configuration of the element circuit.

[0035] As can be seen from FIG. 10 , the element circuit is provided on the substrate 102 directly or via an undercoat 116 of an optional configuration. There are no restrictions on the structure of the transistors included in the element circuit, and bottom-gate transistors, top-gate transistors, or both may be used. Alternatively, the transistor may be a transistor having gate electrodes above and below a semiconductor film. The transistor 140 illustrated in FIG. 10 is a bottom-gate transistor and is composed of a gate electrode 142, a gate insulating film 144 on the gate electrode 142, a semiconductor film 146 on the gate insulating film 144, and a pair of terminals 148 and 150 on the semiconductor film 146. A planarization film 154 is provided on the transistor 140, and the radio wave reflecting element 120 is formed thereon. As an optional configuration, an interlayer insulating film 152 may be provided between the transistor 140 and the planarization film 154.

[0036] The gate electrode 142, gate insulating film 144, semiconductor film 146, terminals 148 and 150 constituting the transistor 140, as well as the interlayer insulating film 152 and planarization film 154 covering the transistor 140, can be formed using known materials and by appropriately applying known methods, and therefore detailed description thereof will be omitted. Briefly, the gate electrode 142 and terminals 148 and 150 are formed by forming a film containing a metal such as tantalum, molybdenum, titanium, or aluminum using a sputtering method, CVD method, or the like, and then appropriately patterning the film using a photolithography process. The semiconductor film 146 is formed as a film containing a Group 14 element such as silicon, or a film containing an oxide of a Group 13 element such as indium or gallium. The semiconductor film 146 may also be formed by applying a sputtering method or a CVD method. The gate insulating film 144 and interlayer insulating film 152 contain a silicon-containing inorganic compound such as silicon oxide or silicon nitride, and are formed by applying a sputtering method or a CVD method. The planarization film 154 contains a polymer such as an acrylic resin, an epoxy resin, a polyimide, a polyamide, or a silicone resin, and can be formed by appropriately using a wet film-forming method such as a spin coating method, an inkjet method, or a printing method. By providing the planarization film 154, the radio wave reflecting element 120 can be formed on a flat surface. The patch electrode 122 is electrically connected to the transistor 140 through an opening provided in the interlayer insulating film 152, the planarization film 154, or the like, and thereby a control potential is supplied from the signal line driving circuit 114 to the radio wave reflecting element 120.

[0037] As described above, in the radio wave reflecting device 100 of this modified example, the potentials of the patch electrodes 122 of the multiple radio wave reflecting elements 120 can be individually controlled by using an element circuit. Therefore, the dielectric constants of the liquid crystal layers 126 of the multiple radio wave reflecting elements 120 can also be individually controlled. As a result, the phase change of the reflected wave can also be controlled for each radio wave reflecting element 120, and the reflection direction of the radio wave can be controlled two-dimensionally. In other words, the incident radio wave can be reflected at an angle rotated around two axes extending in the column and row directions of the multiple radio wave reflecting elements 120.

[0038] In this example, the results of a simulation study of the influence that the widths of the slits 122b and 130a of the patch electrode 122 and common electrode 130 that constitute the radio wave reflecting element 120 have on the radio wave reflecting characteristics will be described.

[0039] A schematic diagram of the evaluated model element 1 is shown in FIG. 11A, and schematic diagrams of model elements 2 to 4 are shown in FIG. 11B. In each of FIGS. 11A and 11B, the left side is a schematic top view, and the right side is a schematic end view. Model elements 1 to 4 were configured with a square patch electrode 122 (2.8 cm × 2.8 cm) and a common electrode 130 (3.7 cm × 3.7 cm), and a liquid crystal layer 126 sandwiched between them. The electrical conductivity and relative permittivity of the patch electrode 122 and the common electrode 130 were set to 3.5 × 10, respectively. 7 The dielectric constant of the liquid crystal layer 126 was set to 5.4 (S / m), the dielectric constant of the liquid crystal layer 126 was varied between 2.5 and 3.5, and the thickness of the liquid crystal layer 126 was set to 40 μm. Model element 1 had a patch electrode 122 and a common electrode 130 without slits. Meanwhile, model elements 2 to 4 had overlapping slits 122b and 130a of the same width in the patch electrode 122 and the common electrode 130, respectively. The widths of the slits 122b and 130a (space widths S1 and S2) and the distances between adjacent slits 122b and 130a (line widths L1 and L2) are shown in Table 1 below. From Table 1, the line-space ratios of model elements 2 to 4 are all 1, and therefore the aperture ratios of these model elements are all 50%. Meanwhile, the aperture ratio of model element 1 is 0%.

[0040] The simulation results are shown in Figure 12. The vertical axis of the graph shown in Figure 12 represents the attenuation of the amplitude of the reflected wave in common logarithm, with smaller values ​​indicating stronger absorption of the radio wave, i.e., a reduction in reflectivity. The right vertical axis of Figure 12 indicates the amount of phase change of the incident radio wave, with larger amounts of phase change indicating a larger reflection angle than the angle of incidence. In other words, the larger the value on the right vertical axis, the greater the change in the reflection angle. In both plots, the leftmost point is the simulation result for model element 1.

[0041] As can be seen from the results of Fig. 12, although the decrease in reflectivity and the amount of phase change decrease as the space width of slits 122b and 130a increases, by making the width of slits 122b and 130a smaller than a certain value, it is possible to ensure high reflectivity and phase change amounts comparable to those of model element 1 which does not have slits. The results of Fig. 12 suggest that when the line-space ratios L1 / S1 and L2 / S2 are 1, if the width of slits 122b and 130a is 30 µm or less, it is possible to achieve both a high aperture ratio and excellent radio wave reflection characteristics.

[0042] In this way, by setting L1 / S1 and L2 / S2 relatively low and adjusting the widths of the slits 122b and 130a (i.e., the space widths S1 and S2) to be relatively small, it is possible to provide a radio wave reflecting device that combines a high aperture ratio and excellent radio wave reflection characteristics. Therefore, according to the embodiment of the present invention, it is possible to provide a light-transmitting radio wave reflecting device that does not spoil the scenery.

[0043] The above-described embodiments of the present invention can be combined as appropriate as long as they are not mutually contradictory. Furthermore, based on the radio wave reflecting element or radio wave reflecting device of each embodiment, a person skilled in the art can add or delete components or change the design as appropriate, or add or omit processes or change conditions, and these will also be included in the scope of the present invention as long as they include the gist of the present invention.

[0044] Even if there are other effects and advantages different from those brought about by the aspects of each of the above-mentioned embodiments, those that are clear from the description in this specification or that can be easily predicted by a person skilled in the art are naturally understood to be brought about by the present invention.

[0045] 100: radio wave reflecting device, 102: substrate, 104: opposing substrate, 106: sealing material, 110: terminal, 112: gate line driving circuit, 114: signal line driving circuit, 116: undercoat, 118: overcoat, 120: radio wave reflecting element, 122: patch electrode, 122a: connecting portion, 122b: slit, 124: first alignment film, 126: liquid crystal layer, 128: second alignment film, 130: common electrode, 130a: slit, 140: transistor, 142: gate electrode, 144: gate insulating film, 146: semiconductor film, 148: terminal, 150: terminal, 152: interlayer insulating film, 154: planarization film

Claims

1. A radio wave reflecting device comprising a plurality of radio wave reflecting elements arranged in a matrix having a plurality of rows and a plurality of columns, each of the plurality of radio wave reflecting elements comprising: a patch electrode having a plurality of first slits that are parallel to each other, have the same width as each other, and extend in either the row direction or the column direction; a first orientation film on the patch electrode; a liquid crystal layer on the first orientation film; a second orientation film on the liquid crystal layer; and a common electrode located on the second orientation film, having a plurality of second slits that are parallel to the plurality of first slits and have the same width as the plurality of first slits, wherein in each of the plurality of radio wave reflecting elements, the distance between adjacent first slits is constant and is the same as the distance between adjacent second slits.

2. A radio wave reflecting device as described in claim 1, wherein in each of said plurality of radio wave reflecting elements, the ratio of the distance between adjacent first slits to the width of said first slits is not less than 0.05 and not more than 4.

0.

3. A radio wave reflecting device as described in claim 1, wherein in each of said plurality of radio wave reflecting elements, the ratio of the distance between adjacent first slits to the width of said first slits is not less than 0.05 and not more than 1.

0.

4. The radio wave reflecting device according to claim 1, wherein the width of the plurality of first slits is not less than 0.1 μm and not more than 30 μm.

5. The radio wave reflecting device according to claim 1, wherein the width of the plurality of first slits is equal to or greater than the distance between adjacent first slits.

6. The radio wave reflecting device according to claim 1, wherein the patch electrodes located in the same row are electrically connected to each other.

7. The radio wave reflecting device according to claim 1, wherein the patch electrodes located in the same row are electrically connected to each other.

8. The radio wave reflecting device according to claim 1, wherein each of said plurality of radio wave reflecting elements further comprises a transistor electrically connected to said patch electrode.

9. The radio wave reflecting device according to claim 1, wherein the common electrodes located in the same column are electrically connected to each other.

10. The radio wave reflecting device according to claim 1, wherein the common electrodes located in the same row are electrically connected to each other.

11. The radio wave reflecting device according to claim 1, wherein all of said common electrodes of said plurality of radio wave reflecting elements are electrically connected to each other.

12. The radio wave reflecting device according to claim 1, wherein in each of said plurality of radio wave reflecting elements, said patch electrode and said common electrode contain a zero-valent metal.

13. The radio wave reflecting device according to claim 1, wherein in each of said plurality of radio wave reflecting elements, said plurality of first slits overlap with said plurality of second slits.

14. The radio wave reflecting device according to claim 1, wherein in each of said plurality of radio wave reflecting elements, at least one of said plurality of first slits overlaps with an area between adjacent said second slits.

15. A radio wave reflecting device as described in claim 1, wherein in each of said plurality of radio wave reflecting elements, at least one of said plurality of first slits overlaps with said second slit and an area between said adjacent second slits.

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